Primer for cured silicone release agents

ABSTRACT

A composition useful as a coupling agent for promoting the adhesion of a cured organopolysiloxane release agent to a cellulosic substrate is the reaction product of WHERE R is a divalent or trivalent radical of carbon and hydrogen, R&#39;&#39; is a lower alkyl, n is 1 to 2 and R&#39;&#39;&#39;&#39; is a monovalent hydrocarbon radical. An example is a reaction product of AND VINYLTRIACETOXYSILANE.

United States Patent 51 3,691,206

Northrup 1 Sept. 12, 1972 I54! PRIMER FOR CURED SILICONE 3,264,258 8/1966 Ceyzeriat ..260/46.5

RELEASE AGENTS Hal J. Northrup, c/o Dow Corning Corp., Midland, Mich. 48640 Filed: March 29, 1971 Appl. No.: 129,214

Related US. Application Data Continuation of Ser. No. 739,967, May 22, 1968, which is a division of Ser. No. 491,414, Sept. 29, 1965, Pat. No. 3,427,270.

Inventor:

References Cited UNITED STATES PATENTS 6/1953 Smith-Johannsen 161/93 12/1958 MacKenzie et al. ....260/448.8 7/ 1960 Plueddemann ..260/348 X 2/1963 Ault et a1 ..l17/155 2/1964 Plueddemann ..260/348 Primary Examiner-Norma S. Milestone Attorney-Robert F. Fleming, Jr., Laurence R. l-lobey and Harry D. Dingman [57] ABSTRACT A composition useful as a coupling agent for promoting the adhesion of a cured organopolysiloxane release agent to a cellulosic substrate is the reaction product of where R is a divalent or trivalent radical of carbon and hydrogen, R is a lower alkyl, n is l to 2 and R" is a monovalent hydrocarbon radical. An example is a reaction product of o (HkHomocmcmcmsuoonm and vinyltriacetoxysilane.

5 Claims, No Drawings PRIMER FOR CURED SILICONE RELEASE AGENTS This is a continuation of application Ser. No. 739,967, filed May 22, 1968, which is a division of application Ser. No. 491,414, filed Sept. 29, 1965, now US. Pat. No. 3,427,270, issued Feb. 11, 1969.

This application relates to new adhesion promoters for cured organopolysiloxane release agents on cellulosic substrates.

Cured organopolysiloxane release agents are commercially used on various types of paper and cardboard. An example of such a release agent is a hydroxyl-endblocked dimethylpolysiloxane gum crosslinked with a small amount of methylhydrogenpolysiloxane after application to a cellulosic substrate as shown in US. Pat. No. 3,061,567. Examples of other silicone release agents are shown in US. Application Ser. No. 477,304, filed Aug. 4, 1965, now US. Pat. No. 3,445,417 issued May 20, 1969.

The organopolysiloxane release agents have, however, a tendency of being removable from their substrates by abrasion due to a weak bond between the release agent and substrate. A number of primers have been developed to improve the adhesion of the release agents to their substrates, including the epoxyacyloxysilanes of US. Pat. No. 3,120,546.

This application relates to a coupling agent for promoting the adhesion of a cured organopolysiloxane release agent to a cellulosic substrate consisting essentially of the reaction product of from 25 to 75 weight per cent of a. a silane of the formula C n CHI ZSKORM and from 25 to 75 weight per cent of b. a silane ofthe formula II rv'suoooHm where R is a divalent or trivalent radical consisting of carbon and hydrogen, any other atoms present being oxygen in an ether or carboxylic ester linkage,

R is a lower alkyl radical,

n has a value of l to 2, and

R" is a monovalent hydrocarbon radical of no more than 3 carbon atoms,

R being trivalent when n has a value of l and divalent when n has a value of 2.

The coupling agents of this invention exhibit superiority over the previously known primers in that they provide firm coupling of the silicone release agent to its cellulosic substrate without significantly altering the release properties of the agent, and, additionally, the primer can be added to a solvent solution of the silicone release agent to provide one-step application of primer and release agent, while lengthening the time which elapses before gelation of the release agent occurs in the bath. The previously-known primers fail to consistently yield all of the above advantages, as compared with the primers of this invention.

R can be any radical as defined above, e.g. methylene, ethylene, propylene, butylene, decylene, phenylene, xenylene, cyclohexylene, cyclopentylene, methylcyclohexylene, tolylene and Cl-I CH =Cl-I- CH R can also be any divalent ether radical such as -CH Cl-l OCl-1 Cl-l CH (OC H.,) O(CH -Cl-l OC H OC H and CH OCH CH CH R can also contain a divalent ester linkage derived from a carboxylic acid SUCh as and R can be any lower alkyl radical such as methyl, ethyl, isopropyl, or butyl.

Ingredient (a), therefore, can be any silane such 0 0 CHzCHCILCHqSKOCCH CHzCHCHzOCHgGH-CHS1(O(EH S CHZCHQSKOCHD: CH2CHCH20(C2H40)3CH2OH2OH2 Si(O c3111): omcnOsnoorm,

and

ll c tboncmo o oncmsim 0m),

Examples of ingredient (b) are ll ll CH3Si(O C CH3)3, CHgCHgSKO C CH3); and

wmhonsuoi'zomh Ingredients (a) and (b) spontaneously react with each other to form the reaction product of this invention. The reaction takes about 20 days at room temperature, about 2 hours at C., and about 1 hour at 200C. An unreacted mixture of (a) and (b) does not yield the above-mentioned advantages to the same degree as does their reaction product. The presence of the reaction product can therefore be ascertained by observing a marked improvement in the properties of the composition as a primer for a release agent over a mixture of the separate ingredients.

It should be noted that ingredient (b) is operative alone as a primer for release agents, but several times the amount of (b) alone is required to duplicate the adhesion provided by a given amount of the reaction product of (a) and (b). Furthermore, ingredient (b) alone has a tendency of shortening the gel time of a solution of silicone release agent.

Ingredient (a) alone imparts only a minor improvement in the adhesion of silicone release agents to cellulosic substrates.

The epoxyacyloxysilanes mentioned above give irreproducible and varying results as primers for silicone release agents.

The exact chemical nature of the reaction product of this invention is unknown. It has been observed, however, that most of the epoxy groups of ingredient (a) disappear on formation of the reaction product, while a majority of the acetoxy groups of ingredient (b) are retained. The reaction product would therefore appear to contain some sort of an organic polymer with silyl pendant groups.

A preferred ingredient (a) is a silane of the formula The coupling agents of this invention are generally added to the organopolysiloxane release agent, which is usually dispersed in a volatile solvent such as xylene, perchloroethylene, benzene, octane, cyclohexane, dibutylketone, or dibutylether. This solution, which may also contain a suitable known curing catalyst for the organopolysiloxane release agent, is then applied to the cellulosic substrate and cured after the solvent has evaporated. Examples of suitable curing catalysts are stannous octoate, dibutyltin dilaurate, and tetrabutyl titanate.

Generally, no modifications of the normal techniques for the application and curing of silicone release agents are required when the coupling agents of this invention are used.

A desirable bath for coating a cellulose substrate with a silicone release agent and the coupling agent of this invention consists essentially of (l) 100 parts by weight of a curable organopolysiloxane release agent, (2) from 0.5 to parts by weight of the reaction product of from 25 to 75 weight per cent ofa silane of the formula 0 cmonasito Rex,

and from 25 to 75 weight per cent of (b) a silane of the formula where R is a divalent or trivalent radical consisting of carbon and hydrogen, any other atoms present being oxygen in an ether or carboxylic ester linkage. R is a lower alkyl radical, n has a value of 1 to 2, and R is a monovalent hydrocarbon radical of no more than 3 atoms, R being trivalent when n has a value of l and divalent when n has a value of 2, and (3) from 50 to 20,000 parts by weight of a volatile solvent for l The following examples are illustrative only and should not be construed as limiting the invention, which is properly delineated in the appended claims.

EXAMPLE 1 To several samples consisting of about 29 parts by weight of a hydroxyl-endblocked dimethylpolysiloxane having a viscosity at 25C. of about 8,000 cs., 1 part of a composition of the formula The product was a paper which was coated with a thin film of cured, elastomeric silicone which exhibited excellent release properties. This silicone film was vigorously rubbed with the finger to see whether it would rub off of the paper. The results were as follows:

Coupling Agent Rub-off (a) 0.75 part each of vinyltriacetoxysilane and none c monomowmnsnocmn previously heated together for l6 hours at 250F.

0.75 part each of ethyltriacetoxysilane and none previously heated together for 16 hours at (c) 0.75 part each of methyltriacetoxysilane and none previously heated together for l6 hours at 250F.

0.14 part of vinyltriacetoxysilane and 0.40 part of none heated 4 hours at F. and 1 hour at 250F.

0.40 part of vinyltriacetoxysilane and 0.14 part of none 0 o nknoniotomnsuoomn heated 4 hours at 175F. and 1 hour at 250F.

similar to (a), but without prior heating 075 part of methyltriacetoxysilane 0.75 part of very slight slight considerable Runs (f) through (h) are included to show the superiority of the coupling agents of this invention (runs (a) through (e)).

The remaining portions of the solutions used in runs ((1) and (e) above were allowed to stand at room temperature for 96 hours. They were still both ungelled and useable at the end of this period.

Identical solutions which contained no coupling agent, or which contained only an organotriacetoxysilane coupling agent gelled in 6 to 24 hours at room temperature.

EXAMPLE 2 When the following amounts of the following coupling agents are added to mixtures of 100 g. of

1 i SiO H,4g.oi(CHa)zS1O sio suonm,

CH H

Amount Coupling Agent (a) l g. Equal wts. of isopropyltriacetoxysilane and rfincnomomonomsuo02m):

heated for 2 hours at 400F. (b) 7 g. 4 g. of n-propyltriacetoxysilane and 3 g. of

c morrcmooomomsuo c8111):

heated for 1 hour at 500F. (c) 3 g. Equal wts. of ethynyltriacetoxysilane and O\ ,CHz(l)HCHzSi(0CH3)3 heated for 24 hours at [50F That which is claimed is:

l. A coupling agent for promoting the adhesion of a cured organopolysiloxane release agent to paper and cardboard consisting essentially of the reaction product obtained after from 20 days at room temperature to l hour at 260C. of from 25 to 75 weight per cent of a. a silane of the formula 0 o H, cHRs1 011m, 10

and from 25 to 75 weight per cent of b. a silane of the formula o rv'suoiicmn where R is a divalent radical selected from the group consisting of methylene, ethylene, propylene, butylene, decylene, phenylene, xenylene, cyclohexylene, cyclopentylene, methylcyclohexylene, tolylene, CH CI-l CHCl-l CH CH OCH CH CH; CH1CH:O (ilHCH CH OCH CH CH, CH OOCCH CH CH OOC(CH 6-,

CHI! cn ooccncfll CH (OC H 0OCCH Cl-1 -CH O(C H O) C H C1-l C1-l (IT-[:1 cH,coogH g:H..

-Cl-l OCH CH C1-l |CH3 cHlcHoHcH= 5O and CH COOCl-l CH R is a lower alkyl radical and R" is a monovalent hydrocarbon radical of no more than three carbon atoms selected from the group consisting of methyl, ethyl, isopropyl, n-propyl, vinyl and ethynyl. 2. The coupling agent of claim 1 where (a) is O CHzCHCHzO CHzCHzCHzSKO CH3);

3. The coupling agent of claim 2 where (b) is vinyltriacetoxysilane.

4. The coupling agent of claim 2 where (b) is methyltriacetoxysilane.

S. The coupling agent of claim 2 where (b) is ethyltriacetoxysilane. 

2. The coupling agent of claim 1 where (a) is
 3. The coupling agent of claim 2 where (b) is vinyltriacetoxysilane.
 4. The coupling agent of claim 2 where (b) is methyltriacetoxysilane.
 5. The coupling agent of claim 2 where (b) is ethyltriacetoxysilane. 